1. Field of the Invention
The present invention relates to a printing medium coating solution to be partly or entirely applied onto a surface of a printing medium before or after an image is at least partly formed on the printing medium through an ink-jet recording method or the like. Further, the present invention relates to an ink-jet ink used for an ink-jet recording method including image recording through ink ejection. Further, the present invention relates to an image forming method for forming an image by using the printing medium coating solution and the ink-jet ink. Further, the present invention relates to a set of the printing medium coating solution and the ink-jet ink. Further, the present invention relates to an ink-jet recording apparatus equipped with the set of the printing medium coating solution and the ink-jet ink.
2. Related Background Art
The ink-jet recording method is a method allowing fine droplets of ink to fly and adhere onto a printing medium (such as paper) based on various operational principles for recording of an image or a letter. The ink-jet recording method has such a feature that the method allows high speed recording, produces little noise, facilitates multi-coloring, has high flexibility in recording patterns, and requires no developing or fixing, and therefore has rapidly spread in various applications. However, use of plain paper as a printing medium may cause a curling phenomenon including warping or curling of the paper. The curling phenomenon greatly results from provision of moisture. That is, it is known that provision of moisture over a large area and provision of a large amount of moisture cause a significant curling phenomenon.
Several methods have been heretofore proposed to reduce and suppress curling phenomenon. For example, there is proposed an ink-jet ink containing a solid substance having four or more hydroxyl groups in a molecular structure and capable of dissolving in water or an aqueous organic solvent (see JP 4-332775 A, for example). Further, there is proposed an ink containing an anti-curling agent such as sugars, sugar alcohols, or a specific amide compound (see JP 6-157955 A, JP 6-240189 A, JP 9-16539 A, and JP 9-176538 A, for example). Further, there is proposed an ink containing a specific polyalcohol and glycerin in combination (see JP 10-130550 A, for example). Further, there is proposed an ink containing a solvent, a polymer binder, a mordant, a water-soluble anti-curling agent compound, a water-soluble desizing compound, a light resistant compound, a defoaming agent, and the like (see JP 2000-19826 A, for example).
Further, there are proposed various methods for forming an image as a measure for forming an image through an ink-jet recording method including preparation of a liquid (coating solution) for forming a favorable image separately from a normal ink-jet ink as described above; and adherence of the liquid onto a printing medium before ink ejection. For example, there is proposed a recording method (hereinafter, referred to as a two-liquid system) including provision of a liquid composition containing polyvalent metal ions to a printing medium in advance; and subjecting the printing medium to printing by using an ink having reactivity with the liquid composition, to thereby attain improvement in image properties such as uniformity of image and image density (see JP 9-234943 A, JP 11-115303 A, and JP 2000-94825 A, for example).